Many printing technologies, such as xerography and ink-jet printing, exploit a rotatable imaging member on which an image is first created with marking material, such as liquid ink or powdered toner, and then transferred to a print sheet. When controlling such a printing apparatus, it is common to place on the imaging member at various times test patches, meaning areas of marking material of predetermined desired properties such as optical density, and then measuring the actual properties of each test patch as part of an overall control process.
In some embodiments of printing apparatus, the test patches are placed on the imaging member, and tested for certain properties; but the marking material forming each test patch is never transferred to a print sheet. In such cases, the marking material forming the test patches has to be cleaned off, such as by a cleaning device within the apparatus. In some situations, the imaging member has to cycle multiple times past the cleaning device to remove the marking material sufficiently from the patch area. On the intermediate cycles before the marking material on the test patch is completely removed, the area around the test patch cannot be used for placing of images.
U.S. Pat. Nos. 6,167,217 and 6,385,408 disclose basic systems for scheduling the creation of test patches in a xerographic printer. U.S. Pat. No. 5,173,733 shows a system for disabling page-sized areas on a photoreceptor in response to detecting imperfections on the photoreceptor.